1. Field of the Invention
The present invention relates to an endoscope system and a control method for the same. More particularly, the present invention relates to an endoscope system in which normal and specific light can be selectively utilized for precise imaging of an object in a body cavity, and a control method for the same.
2. Description Related to the Prior Art
An electronic endoscope is widely used for a diagnosis by medical examination in the field of medical instruments. The endoscope includes a head assembly for entry in a body cavity. A solid-state image pickup device is incorporated in the head assembly, such as a CCD image sensor and the like. There are a processing apparatus and a light source to both of which the endoscope is connected by use of a cable, connector or the like.
The processing apparatus processes an image signal from the image pickup device in processing of various functions, and produces image data of an endoscopic image for use in the diagnosis. A display panel in connection with the processing apparatus is driven to display the image. The light source contains a white light source such as a xenon lamp, and emits illumination light for application to an object in the body cavity.
The NBI (Narrow band imaging) is known in the field of the diagnosis by use of the endoscope to facilitate discovery of lesions. Specific light of a narrow wavelength of a predetermined band is applied to an object of interest, with a difference from normal light of white color characteristically having a broad wavelength. Reflected light of the specific light is evaluated for imaging of a specific image, which is distinct from a normal image obtained under a condition with the normal light. In the narrow band imaging (NBI), special images can be easily created without coloring the object with color dye, injection of angiography contrast medium such as indocyanine green (ICG), or the like, for example, the images with enhancement of submucosa blood vessels, and with enhancement of structures of organs such as stomach walls and surface tissue of intestines.
Specific methods of the narrow band imaging (NBI) are disclosed in U.S. Pat.Pub. No. 2003/176768 (corresponding to JP-A 2002-095635) and U.S. Pat. No. 5,667,474 (corresponding to JP-A 7-246184). An optical filter assembly for use includes a filter for the normal light and a filter for the specific light, and is disposed in a light path of the light from the light source. A motor or other mechanism shifts the filter assembly when an operator or doctor manually operates a button or the like for changeover, to create the normal and specific images by imaging.
U.S. Pat.Pub. No. 2003/176768 discloses use of a rotary filter in the endoscope for outputting the normal and specific light. In one embodiment of this document, elongation of the storage time of the image pickup device is suggested in imaging with the specific light for the purpose of compensating for reduction of an amount of light even upon changeover to the specific light. Blur of an image will occur seriously with the elongation of the storage time. In view of this, a motion detector for detecting motion of the object of interest is incorporated. If no motion is detected in a period of freeze-frame operation, an image in an image memory is renewed. If motion of the object is found, the renewal of the image memory is disabled. Furthermore, in a certain embodiment of the same document, a xenon lamp is suggested as light source of the normal light, a super high pressure mercury lamp is suggested as light source of the specific light.
U.S. Pat. No. 5,667,474 includes an optical instrument having the filter assembly and the motion detector in a manner similar to U.S. Pat.Pub. No. 2003/176768. If motion of the object of interest is detected before imaging with the normal light, the freeze-frame operation is disabled. If motion of the object is detected before imaging with the specific light, addition of preceding and succeeding frame images (noise reduction) is disabled. If no motion of the object is detected before imaging with the specific light, addition of preceding and succeeding frame images (noise reduction) is carried out.
In the narrow band imaging (NBI), it has been impossible in the diagnosis visually to compare the normal and specific images by simultaneous display on a display panel. This is due to a time difference between imaging of the normal and specific images. If the object of interest relatively moves between time points of the imaging of those, no simultaneity is kept between the two to cause failure in precise comparison.
In U.S. Pat.Pub. No. 2003/176768 and U.S. Pat. No. 5,667,474, the filter assembly is shifted mechanically to change over the display form of each of the normal and specific images in an exclusive manner. There is no suggestion of simultaneity, or closeness in the time of imaging of the normal and specific images. Although relative motion of the object of interest is detected, U.S. Pat.Pub. No. 2003/176768 only discloses determination of renewal of image data at the time of the freeze-frame operation. U.S. Pat. No. 5,667,474 only discloses inhibition of the freeze-frame operation and allowance of the noise reduction. Precise comparison between the normal and specific images is not suggested in known techniques of endoscope system.